U.S. patent application number 13/287334 was filed with the patent office on 2013-05-02 for machine, control system and method for hovering an implement.
This patent application is currently assigned to CATERPILLAR, INC.. The applicant listed for this patent is David C. Atkinson. Invention is credited to David C. Atkinson.
Application Number | 20130108403 13/287334 |
Document ID | / |
Family ID | 48172630 |
Filed Date | 2013-05-02 |
United States Patent
Application |
20130108403 |
Kind Code |
A1 |
Atkinson; David C. |
May 2, 2013 |
Machine, Control System And Method For Hovering An Implement
Abstract
A machine such as a wheel loader includes a frame and ground
engaging propulsion elements coupled with the frame. A
hydraulically actuated implement system of the machine includes a
linkage and an implement and is adjustable from a starting
configuration to a second configuration according to a substrate
collision avoiding pattern. In the second configuration, the
implement hovers above a substrate beneath the machine. Related
methodology and control logic is also disclosed.
Inventors: |
Atkinson; David C.; (Dunlap,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Atkinson; David C. |
Dunlap |
IL |
US |
|
|
Assignee: |
CATERPILLAR, INC.
Peoria
IL
|
Family ID: |
48172630 |
Appl. No.: |
13/287334 |
Filed: |
November 2, 2011 |
Current U.S.
Class: |
414/685 ;
701/50 |
Current CPC
Class: |
E02F 9/2041 20130101;
E02F 9/265 20130101; E02F 3/434 20130101; E02F 3/439 20130101 |
Class at
Publication: |
414/685 ;
701/50 |
International
Class: |
E02F 9/20 20060101
E02F009/20; E02F 3/36 20060101 E02F003/36; G06F 19/00 20110101
G06F019/00 |
Claims
1. A method of controlling a hydraulically actuated implement
system having a linkage and an implement, in a self-propelled
ground engaging machine, comprising the steps of: electronically
reading a stored value which is linked with a starting
configuration of the implement system, responsive to an implement
hover command; outputting a control signal to the implement system
which is based at least in part on the stored value; and actuating
the implement system responsive to the control signal, such that
the implement system moves according to a substrate collision
avoiding pattern from the starting configuration to a second
configuration at which the implement hovers above a substrate
beneath the machine.
2. The method of claim 1 further comprising a step of receiving the
implement hover command while the linkage is raised, and wherein
the step of actuating further includes lowering the implement
system from the starting configuration to the second
configuration.
3. The method of claim 2 further comprising a step of receiving
data indicative of a starting linkage state, the starting
configuration being defined at least in part by the starting
linkage state from among a plurality of possible starting
configurations.
4. The method of claim 3 wherein the linkage includes a lift arm
and the implement includes a bucket, and wherein the step of
receiving data further includes receiving data indicative of
position, travel speed, and travel direction, of the lift arm.
5. The method of claim 4 wherein the step of actuating further
includes tilting the bucket responsive to the starting linkage
state.
6. The method of claim 3 wherein the step of electronically reading
further includes reading the stored value at an address having a
starting linkage state coordinate.
7. The method of claim 6 wherein the step of electronically reading
further includes reading the stored value at an address having an
implement type coordinate.
8. The method of claim 6 wherein the step of electronically reading
includes reading a stored gain.
9. The method of claim 8 wherein the step of receiving the
implement hover command includes receiving the command from an
operator input device having a total of two different states.
10. The method of claim 1 wherein the step of actuating further
includes actuating the implement system such that the implement
hovers at a height above the substrate which is less than about 5%
of a maximum lift height of the implement, during forward travel of
the machine.
11. A control system for a hydraulically actuated implement system
having a linkage and an implement, in a self-propelled ground
engaging machine, comprising: a computer readable memory storing a
value linked with a starting configuration of the implement system;
an electronic control unit coupled with the computer readable
memory and configured to read the stored value, in response to an
implement hover command; and the electronic control unit being
further configured to output a control signal to the implement
system which is based at least in part on the stored value, such
that the implement system moves according to a substrate collision
avoiding pattern from the starting configuration to a second
configuration at which the implement hovers above a substrate
beneath the machine.
12. The control system of claim 11 wherein the value is one of a
plurality of values stored on the computer readable memory and each
being linked to a different one of a plurality of possible starting
configurations of the implement system.
13. The control system of claim 12 wherein each of the plurality of
stored values has an address on the computer readable memory
including a starting linkage position coordinate, whereby the
plurality of stored values are linked to the plurality of possible
starting configurations.
14. The control system of claim 12 wherein the electronic control
unit is further configured to receive data indicative of a throttle
position in the machine and to output the control signal responsive
to the data indicative of throttle position.
15. The control system of claim 12 wherein the value includes a
stored gain.
16. The control system of claim 12 further comprising a sensor
configured to sense a position of the linkage, and wherein the
electronic control unit is coupled with the sensor and configured
to read the stored value responsive to a sensed starting position
of the linkage.
17. The control system of claim 16 wherein the electronic control
unit is further configured to output the control signal to a
control valve for a lift actuator of the linkage and to output
another control signal to a control valve for a tilt actuator of
the implement.
18. The control system of claim 17 wherein the substrate collision
avoiding pattern is defined in part by a speed of rotation of the
linkage about a pivot axis with the machine and in part by a speed
of rotation of the implement about a pivot axis with the linkage,
and wherein the electronic control unit is further configured to
output the another control signal such that a commanded speed of
the implement is responsive to a commanded speed of the
linkage.
19. A machine comprising: a frame; ground engaging propulsion
elements coupled with the frame; a hydraulically actuated implement
system having a linkage and an implement; an electronic control
unit in control communication with the implement system and
configured to adjust the implement system from a starting
configuration to a second configuration at which the implement
hovers above a substrate beneath the machine; and the electronic
control unit being further configured to receive data indicative of
the starting configuration and responsively adjust the implement
system to the second configuration according to a substrate
collision avoiding pattern.
20. The machine of claim 19 comprising a wheel loader wherein the
linkage includes a lift arm and the implement includes a bucket,
and further comprising a sensor group configured to sense a
position of the lift arm and a position of the bucket in a
reference frame defined by the machine; and wherein the electronic
control unit is further configured to adjust the implement system
to the second configuration responsive to the sensed positions such
that the implement hovers at a height above the substrate which is
less than about 5% of a maximum lift height of the implement.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to
electro-hydraulic control strategies for implement systems in
ground engaging machines, and relates more particularly to
controllably hovering an implement above a substrate beneath a
machine.
BACKGROUND
[0002] Hydraulically actuated implement systems of many different
types are used in a broad variety of machines. Track-type tractors,
backhoes, excavators, and wheel loaders are notable examples,
having hydraulically actuated implement systems for digging,
dozing, loading, spreading and all manner of other activities
relating to manipulation of loose material and various other types
of loads. Controlling a hydraulically actuated implement system
with even reasonable efficiency and accuracy is by no means simple.
Operators are typically tasked with manually manipulating various
control levers while monitoring multiple operating conditions of
the machine, whether stationary or traveling. It is thus
unsurprising that even highly skilled operators with decades of
experience are often able to improve performance with the
assistance of various electronically controlled features of
hydraulically actuated implement systems.
[0003] Over the years, engineers have proposed a great many
different strategies for automating work cycles or parts thereof,
such as material loading cycles whereby a machine captures, lifts
and dumps material. Rather than requiring an operator to manually
and repetitiously raise and lower the machine's lift arms, control
tilting of the machine's bucket, and monitor and control the travel
path and speed of the machine itself, a computer controls some or
all of the functions of the implement system so that an operator
can focus his attention elsewhere, or simply avoid fatigue.
[0004] Other examples of computer controlled processes include
grading, trenching, and virtually any other common activity which
can be performed by a human operator. Despite substantial advances
in automated machine process technology, there nevertheless remain
many instances where skilled operators can best computers in
relation to at least certain aspects of a machine process, or where
handing over control of an implement system to a computer for the
totality of a work cycle is undesirable for other reasons. In still
other instances, designing and implementing computer control for
all aspects of a work cycle has proven to be very challenging, and
often unnecessary to achieve real world efficiency gains. There
thus remain ample opportunities for automating parts of machine
work cycles, while leaving other parts to be controlled
conventionally by an operator or by a separate control routine.
[0005] One example of an automated control strategy for a
construction machine is known from U.S. Pat. No. 5,052,883 to
Morita et al. In Morita et al., a work vehicle has an implement
position controller. The controller is configured to automatically
orient and position an implement, such as a bucket coupled with a
linkage in a wheel loader. While Morita et al. appears to be an
elegant strategy for attaining a pre-defined bucket orientation and
position, especially for certain types of work cycles, there is
always room for improvement, especially as new problems are
recognized or created.
SUMMARY
[0006] In one aspect, a method of controlling a hydraulically
actuated implement system having a linkage and an implement, in a
self-propelled ground engaging machine, includes electronically
reading a stored value which is linked with a starting
configuration of the implement system, responsive to an implement
hover command, and outputting a control signal to the implement
system which is based at least in part on the stored value. The
method further includes actuating the implement system responsive
to the control signal, such that the implement system moves
according to a substrate collision avoiding pattern from the
starting configuration to a second configuration at which the
implement hovers above a substrate beneath the machine.
[0007] In another aspect, a control system for a hydraulically
actuated implement system having a linkage and an implement, in a
self-propelled ground engaging machine, includes a computer
readable memory storing a value linked with a starting
configuration of the implement system. The control system further
includes an electronic control unit coupled with the computer
readable memory and configured to read the stored value, in
response to an implement hover command. The electronic control unit
is further configured to output a control signal to the implement
system which is based at least in part on the stored value, such
that the implement system moves according to a substrate collision
avoiding pattern from the starting configuration to a second
configuration at which the implement hovers above a substrate
beneath the machine.
[0008] In still another aspect, a machine includes a frame and
ground engaging propulsion elements coupled with the frame. The
machine further includes a hydraulically actuated implement system
having a linkage and an implement, and an electronic control unit
in control communication with the implement system. The electronic
control unit is configured to adjust the implement system from a
starting configuration to a second configuration at which the
implement hovers above a substrate beneath the machine. The
electronic control unit is further configured to receive data
indicative of the starting configuration and responsively adjust
the implement system to the second configuration according to a
substrate collision avoiding pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a side diagrammatic view of a machine, according
to one embodiment;
[0010] FIG. 2 is a diagrammatic view of a hydraulically actuated
implement system, and control system therefor, according to one
embodiment;
[0011] FIG. 3a is a side diagrammatic view of the machine of FIG. 1
at one stage of a work cycle, according to one embodiment;
[0012] FIG. 3b is a side diagrammatic view of a machine operated
according to a conventional control strategy and illustrating
collision of an implement with a substrate;
[0013] FIG. 3c is a side diagrammatic view of the machine of FIG. 1
at another stage of the work cycle;
[0014] FIG. 3d is a side diagrammatic view of the machine of FIG. 1
at yet another stage of the work cycle;
[0015] FIG. 3e is a side diagrammatic view of the machine of FIG. 1
at yet another stage of the work cycle;
[0016] FIG. 3f is a side diagrammatic view of the machine of FIG. 1
at yet another stage of the work cycle; and
[0017] FIG. 4 is a flowchart illustrating a control process
according to one embodiment.
DETAILED DESCRIPTION
[0018] Referring to FIG. 1, there is shown a self-propelled,
ground-engaging machine 10 according to one embodiment. Machine 10
includes a frame 16 having a front frame unit 18, a back frame unit
20, and an articulation joint 22 coupling together frame units 18
and 20. An internal combustion engine 28 is mounted to frame 16, as
is an operator cab 26. A set of ground engaging propulsion elements
14 are coupled with frame 16 in a conventional manner for
propelling machine 10. In the illustrated embodiment, propulsion
elements 14 are shown as wheels, however, tracks might be used in
an alternative embodiment. A hydraulically actuated implement
system 12 is coupled with frame 16, and includes a linkage 34
coupled with an implement 36. Linkage 34 may include a plurality of
lift arms, one of which is visible in FIG. 1, but might include a
single lift arm or boom in certain embodiments. Linkage 34 may be
raised and lowered relative to frame 18 about a pivot axis 42,
whereas implement 36 may be rotated about another pivot axis 34
relative to linkage 34.
[0019] Machine 10 may further include a hydraulic system 30 which
includes a lift actuator 38 configured to raise and lower linkage
34 relative to frame 18, and a tilt actuator 40 configured to
rotate implement 36 relative to linkage 34. Actuators 38 and 40 may
be connected via hydraulic lines (not shown) with other components
of hydraulic system 30 for supply and return of fluid in a
conventional manner. In the illustrated embodiment, implement 36
includes a bucket, but in alternative embodiments could include a
fork, a blade, a rotary broom or still another type of implement. A
substrate protection pad 46 may be coupled with implement 36 for
contacting a substrate 200 beneath machine 10. Substrate protection
pad 46 may include a rubber pad adapted to prevent scraping,
scuffing or other damage to substrate 200, as well as preventing
damage to implement 36 itself when machine 10 travels across
substrate 200 with implement system 12 in a fully lowered
position.
[0020] An operator control station 24 may be located in cab 26, for
controlling and operating various aspects of machine 10, including
a set of control levers 52/54, one of which is shown in FIG. 1, a
throttle 67 and an operator input device 68. The operator
controlled devices of control station 24 may connect with a control
system 70 for machine 10, which is configured for controlling
various aspects of operation of implement system 12 as further
described herein.
[0021] Control system 70 may include a computer readable memory 72,
and an electronic control unit 74 coupled with computer readable
memory 72. Control system 70 may further include a group of
sensors, including a first sensor 76 configured to sense a position
of actuator 38, and a second sensor 78 configured to sense a
position of actuator 40. Each of sensors 76 and 78 may be coupled
with electronic control unit 74 to enable monitoring of a position
of each of linkage 34 and implement 36. While linear position
sensors might be used, in other strategies rotary sensors such as
rotary potentiometers, digital cameras or laser sensors might be
used. In any event, inputs from sensors 76 and 78 to electronic
control unit 74 can enable the monitoring of not only position, but
also travel direction and speed of actuators 40 and 38, and this
position, speed, and travel direction of linkage 34 and implement
36. This enables electronic control unit 74 to determine a
configuration of implement system 12, or monitor a change in
configuration of implement system 12, relative to other parts of
machine 10 and/or relative to substrate 200 at any time, the
significance of which will be apparent in view of the following
description.
[0022] Referring now also to FIG. 2, there is shown a diagrammatic
view of certain parts of machine 10, including control system 70
and hydraulic system 30. Hydraulic system 30 may include a tank 50
and a pump 48. Hydraulic fluid may be conveyed between tank 50 and
each of actuators 38 and 40 by way of a first head-side conduit 60
and a second head-side conduit 64, respectively, and a first
rod-side conduit 62 and a second rod-side conduit 66. Hydraulic
system 30 may further include a first control valve 56 for
controlling fluid flow to and from actuator 38, and a second
control valve 58 similarly associated with actuator 40. Each of
control valves 56 and 58 may include a known spool valve which may
be operated directly or indirectly by way of control levers 52 and
54. In one embodiment, each of control valves 56 and 58 may be
electronically controlled, such that manipulating the corresponding
control lever 52 or 54 sends a control signal to electronic control
units 74, which in turn adjusts a position of the corresponding one
of control valves 56 and 58. To this end, each of control valves 56
and 58 may include one or more electrical actuators 57 and 59,
respectively, which can adjust a position of the corresponding
valve in response to control signals from electronic control unit
74. Electronic control unit 74 may utilize information from sensor
76 and optionally from sensor 78, and in certain instances from
throttle 67, to controllably adjust implement system 12 via control
signals to actuators 57 and 59 such that implement 36 hovers above
substrate 200. Adjusting of implement system 12 may take place
based at least in part upon a starting configuration of implement
system 12 when hovering is commanded. In particular, implement
system 12 may be adjusted in a way which accounts for the starting
configuration such that implement system 12 moves according to a
substrate collision avoiding pattern from the starting
configuration to a second configuration at which implement 36
hovers above substrate 200.
[0023] To this end, memory 72 may store a value linked with a
starting configuration of implement system 12. Electronic control
unit 74 may be configured to read the stored value, in response to
an implement hover command such as a command from operator input
device 68. The starting configuration of implement system 12 may be
understood as a configuration presently occupied by implement
system 12 when hovering is commanded. Implement system 12 may
assume a wide variety of different possible starting
configurations, each defined by a combination of a starting state
of linkage 34 about axis 42 and a starting state of implement 36
about axis 44. The starting linkage state may include linkage
position, travel direction, and/or travel speed, about axis 42. The
implement starting state may include implement position, travel
direction, and/or travel speed about axis 44. Data received by
electronic control unit 74 from sensors 76 and 78 may be indicative
of the starting linkage and implement states, thus enabling
electronic control unit 74 to "know" the starting configuration
when the implement hover command is received. The pattern of moving
implement 36 and linkage 34 through space to reach the second,
hovering configuration may thus account for the starting positions
of linkage 34 and implement 36, as well as travel direction and
travel speed. These factors as well as how in particular electronic
control unit 74 may move implement system 12 in consideration of
these factors will be further apparent and understood from the
following description.
[0024] Electronic control unit 74 may be further configured to
output a control signal to implement system 12 which is based at
least in part on the stored value, such that implement system 12
moves according to the substrate collision avoiding pattern noted
above. More than one control signal may be outputted to adjust
implement system 12 as desired, and multiple control signals to
each of electrical actuators 57 and 59 based upon the stored value
as well as upon feedback from sensors 76 and 78 may be used to
ultimately reach the hovering configuration reasonably quickly and
without colliding with substrate 200. In one embodiment, the stored
value may be one of a plurality of values stored on memory 72 and
each being linked to a different one of a plurality of possible
starting configurations of implement system 12. Thus, while those
skilled in the art will appreciate that the number of different
possible starting configurations might be essentially infinite, the
present control strategy may be understood in at least certain
embodiments as treating the number of possible starting
configurations as finite, and store a value associated with each
one of the finite number of possible starting configurations.
[0025] Each of the plurality of stored values may further include
an address on memory 72 which includes a starting linkage position
coordinate, such as linkage lift height. Thus, the plurality of
stored values may be stored in a look up table which has as one of
its coordinates linkage lift height. Linkage lift height may
therefore be understood as linking each of the stored values to one
of the plurality of possible starting configurations. In the
look-up table example, each of the plurality of stored values may
have an address on memory 74 which might also include a starting
implement position coordinate. It will thus be understood that
starting linkage position or lift height may serve as a basis for
determining how to adjust implement system 12 to the hovering
configuration. In expanded or alternative embodiments, starting
implement position or tilt angle may be used. As noted above,
throttle position may also be factor considered by electronic
control unit 72 in determining control signals to output to one or
both of electrical actuators 57 and 59, hence, the addresses in the
look up table might also include a throttle position
coordinate.
[0026] Those skilled in the art will appreciate that throttle
position may relate to pump speed, in turn relating to actuator
speed. A machine at full throttle can be expected to be capable of
moving implement system actuators faster than at part throttle,
thus affecting what patterns of movement are suitable for adjusting
the implement system to a hovering configuration without colliding
with the substrate. Still other factors considered upon initiating
hovering or serving as the basis for controlling implement system
movement in the manner contemplated herein include linkage and/or
implement speed, travel direction, and possibly still other
factors, as alluded to above. It will thus be understood that upon
commencing the hovering control sequence discussed herein,
electronic control unit 74 may be broadly obtaining a picture of
where implement system 12 is located, and what implement system 12
and the overall machine 10 are currently doing, such that control
signals output to implement system 12 can be tailored to move
implement system 12 in such a manner that collision with substrate
200 is avoided.
[0027] In the interest of minimizing the time it takes to move
various parts of an implement system to a desired position, many
electro-hydraulic control systems are configured such that actuator
speed and thus implement system speed is as fast as practicable. In
other words, in a conventional electro-hydraulic implement system,
it is common for an electronic control unit to command a control
valve to be moved to a position which corresponds to maximum
actuator velocity. Those skilled in the art will appreciate,
however, that were such a control strategy to be used unmodified to
command hovering of an implement relatively close to a substrate,
in at least certain instances there would be a risk that the
linkage or implement would move too slowly too fast, too soon, or
too late to avoid collision of the implement with the substrate.
For instance, if linkage lowering to a hover position is commanded
in an electro-hydraulically controlled machine with the linkage
raised and bucket uncurled, then rapidly lowering the linkage all
the way without curling the bucket out of the way could cause the
bucket to crash into the substrate. Collision could thus occur
unless the bucket is itself commanded to rack back or curl quickly
enough to make it out of the way before the linkage is lowered. The
present disclosure addresses these and other concerns by enabling
at least the linkage, and optionally implement, control signals to
be modified from a default or otherwise calculated such that the
implement system smoothly, and without colliding with the substrate
is adjusted to a hovering configuration. By utilizing a stored gain
for control signals to either or both of actuators 57 and 59,
signals are determined which will move actuators 38 and 40 such
that collision with the substrate is avoided. It will further be
understood that rather than utilizing values stored in a table, an
equation might be utilized which enables control unit 74 to
calculate appropriate control signals for these purposes on the
fly.
[0028] Referring now also to FIG. 3a, there is shown a portion of
machine 10 including implement system 12 as it might appear having
just dumped a load of material from implement 36. Linkage 34 is
raised to or close to a maximum lift height, and implement 36 is
tilted forward, or uncurled, such that material may be dumped from
implement 36 into a truck, pile or the like. From the state shown
in FIG. 3a, an implement hover command may be outputted via
operator input device 68 to initiate adjusting implement system 12
to a hovering configuration. Referring now to FIG. 3b, there is
shown implement system 12 as it might appear where moving of
implement system 12 to a hovering configuration has been commanded
without accounting for the starting configuration of implement
system 12. Linkage 34 has been lowered, but implement 36 has been
tilted, or curled, very little, if at all, from the state shown in
FIG. 3a. As a result, implement 36 has collided with substrate 200.
Another way to understand what is depicted in FIG. 3b, is that
linkage 34 has been lowered more quickly than implement 36 has been
tilted out of the way.
[0029] In FIG. 3c, implement system is shown in a configuration it
might occupy where linkage 34 and implement 36 have both been
adjusted, according to the substrate collision avoiding pattern
discussed herein, such that linkage 34 has lowered part way, and
implement 36 has tilted much or all of the way, needed to assume
the hovering configuration. In FIG. 3d, implement system 12 has
been still further adjusted such that implement 36 hovers above
substrate 200 as machine 10 travels forward to engage with a
material pile 400. In FIG. 3d, implement system 36 hovers at a
distance 202 above substrate 200 which may be as small as a few
inches, for instance, about 12 inches or less. In FIG. 3e, hovering
has been deactivated, for instance in response to the operator
manipulating control levers 52/54, and linkage 34 has begun to be
raised while implement 36 has begun to be racked back, to fill
implement 36 with material from pile 400. In FIG. 3f, implement
system 12 is shown as it might appear where linkage 34 is fully
raised with implement 36 containing a full load of material. From
the state shown in FIG. 3f, machine 10 may be backed away from the
material pile, and implement system 12 returned to a configuration
such as that shown in FIG. 3a to dump the material. In FIG. 3f,
implement 36 is shown at a lift height 204 which is approximately a
maximum lift height, measured via a linear distance from an
outermost tip of substrate protection pad 46 to substrate 200. The
distance 202 shown in FIG. 3d which represents a hovering height
may be equal to about 5% or less of the maximum lift height 204
shown in FIG. 3f.
[0030] Those skilled in the art will appreciate that machine 10 may
be moving forward, backward, or not moving at all, at various of
the stages depicted in FIGS. 3a-f, as well as at other stages of a
capture, lift and dump routine as contemplated herein. Accordingly,
during executing a hovering control cycle as described herein, for
at least certain of the procedures thereof, machine 10 may be
moving. The present disclosure is contemplated to allow an operator
to operate machine 10 with greater efficiency than that possible
without the teachings set forth herein. In particular, an operator
may command implement system 12 to assume a hovering configuration
while backing away from a haul truck which has just received a dump
load from implement 36, and by the time the operator commences
moving machine 10 forward into material pile 400, implement system
12 will have been positioned in the hovering configuration. Rather
than separating the operator's attention among positioning
implement system 12 and controlling speed and travel direction of
machine 10, the positioning of implement system 12 can be turned
over to control system 70. Although the present disclosure is not
thereby limited, these capabilities can be considered to be
especially advantageous in improving efficiency in waste handling
applications. In a conventional waster transfer facility,
collection trucks routinely arrive and dump loose material onto a
substrate such as a relatively smooth and flat concrete floor. A
wheel loader such as machine 10 is commonly used to capture and
lift the loose material deposited via the collection trucks, and
transfer the material into larger haul trucks for transport to a
storage site or the like. An operator may thus be performing very
similar work cycles with machine 10 over and over. It has been
observed that sloppy operation, or operation by inexperienced
operators, often results in damage to implements, to the concrete
floors of waste transfer stations, or results in premature wear of
a substrate protection pad. This is due at least in part to the
relative difficulty of manually controlling an implement system
such that the implement hovers just above a substrate, and instead
the implements are often slid across the transfer station floor. In
view of the general similarity of each work cycle executed by the
operator, and the predictable flatness and smoothness of the waste
transfer floor, the presently described control strategy can hover
implement system 12 based upon sensed positions and other
characteristics of the components of implement system 12 in a
reference frame defined by machine 10. In other words, while in
certain environments such as construction or mining a substrate
beneath a wheel loader or other machine might not be safely assumed
to be smooth and flat, in a waste transfer station the underlying
substrate can generally be assumed to be so. For this reason, it is
unnecessary to directly sense a distance between implement 36 and
substrate 200, and instead implement 36 may be successfully hovered
quite close to substrate 200 based upon sensed positions of linkage
34 and implement 36 relative to machine 10 alone.
INDUSTRIAL APPLICABILITY
[0031] Referring now to FIG. 4, there is shown a flowchart 100
illustrating a control process according to the present disclosure.
The process of flowchart 100 starts at Step 105, and then proceeds
to Step 110 to enable the hover system, in other words initialize
control system 70 for controlling implement system 12 in the manner
described herein. As discussed above, an operator may repeat the
same or a similar work cycle many times during an operating shift
on machine 10. Accordingly, each time an operator captures, lifts,
and dumps material, prior to or during returning to the pile to
capture another load, hovering of implement system 12 may be used,
and the "hover system" may be turned on. In other instances,
hovering capability may be disabled.
[0032] From Step 110, the process may proceed to Step 115, where
electronic control unit 74 may query whether work tool
identification is in use. Different implements may have different
masses, dimensions, and possibly other features which render them
best used via a control strategy that accounts for their unique
characteristics. For example, while one-size-fits-all hovering
control strategies are contemplated herein, since many machines are
capable of using different implements such as differently sized
buckets, optimal efficiency and an accurate specified hover height
may be obtained by considering what type of implement is presently
being used. The use of RF (radio frequency) ID tags on implements
can enable a control system to determine which implement the
machine is currently being used with. To this end, different stored
values linked with starting configuration as described herein may
be used depending upon implement type. In the context of a look up
table, electronic control unit 74 may electronically read a stored
value linked with starting configuration of implement system 12,
where the stored value is located at an address on memory 72 having
an implement type coordinate. Accordingly, where work tool
identification is in use, from Step 115 the process may proceed to
Step 120 to retrieve tool geometry data from the stored table. If
work tool identification is not in use at Step 115, the process may
proceed to Step 117 to use default geometry values. From either of
steps 120 or 117, the process may proceed to Step 125 at which the
operator initiates the hover command.
[0033] As discussed above, the hover command may be initiated via
operator input device 68. In one embodiment, input device 68 might
include a push button, switch or the like, having a total of two
states such as an on state or an off state. In other words, in
contrast to other types of input devices such as control levers
used for controlling actuators 38 and 40, input device 68 may
include a simple switch or button which enables the operator to
output the hover command, and then return their attention to other
aspects of controlling machine 10. From Step 125, the process may
proceed to Step 130 at which electronic control unit 74 may query
whether criteria are met for hover activation. In some instances,
limits might be placed on hovering for certain lift arm or bucket
positions, combinations thereof, ground speeds or machine or
implement travel directions. For example, control system 70 might
be configured such that hover criteria are not satisfied if machine
10 is backing up or traveling above a certain speed. If the
criteria are not met, then the process may proceed from Step 130 to
Step 137 to disable hover, for example stopping linkage and
implement movements via control unit 74. From Step 137 the process
may proceed to Step 139 to display a message such as an alert,
fault or error message via a display screen or other operator
perceptible mechanism at control station 24.
[0034] If, at Step 130, the criteria are satisfied for hover
activation, the process may proceed to Step 135 at which electronic
control unit 74 may query whether operator inputs are detected. At
Step 135, electronic control unit 74 may be understood as
determining whether the operator is attempting to manually
manipulate implement system 12 via control levers 52/54. If yes,
the process may proceed to Step 137 to disable hover. If no, the
process may proceed to Step 140 at which electronic control unit 74
may read linkage position, linkage travel speed, and linkage travel
direction, such as via inputs from sensor 76. Additionally, at Step
140, electronic control unit 74 might also evaluate implement
position, travel speed, and/or travel direction, and/or receive
data indicative of throttle position. While implement system 12
will typically be adjusted from a raised starting configuration to
the hovering configuration, an operator might instead command
adjusting implement system 12 to the hovering configuration from a
fully lowered position at which implement 36 is resting upon
substrate 200. From Step 140, the process may proceed to Step 145
at which electronic control unit 74 may calculate a position error
for both linkage 34 and implement 36. In the case of machine 10
having multiple lift arms, position errors might be calculated for
both lift arms. Another way to understand the determination at Step
145 is that electronic control unit 74 is calculating a difference
between actual linkage and implement positions and desired
positions. From Step 145, the process may proceed to Step 150 at
which electronic control unit 74 queries whether bucket and lift
arm position errors are approximately zero. If yes, this may be
taken as an indication that the hovering set point has been
reached, in which case the process may proceed to Step 137 to
disable hover. If, at Step 150, the bucket and lift arm position
errors are not approximately equal to zero, the process may proceed
to Step 155 to retrieve gain values from the stored look-up table
as discussed herein.
[0035] In many instances, a rate and sequence of implement and
linkage movement commands to actuators 38 and 40 may need to adjust
throughout the range of motion of linkage 12. For instance,
implement 36 may need to be curled or racked back as linkage 34
lowers, to prevent implement 36 from contacting the ground, similar
to the depiction in FIG. 3b where implement 36 has not been
adjusted or not sufficiently adjusted to avoid colliding with
substrate 200. In general terms, a speed of rotation of implement
36 about axis 44 and/or a timing of starting rotation of implement
36 may occur responsive to a starting state of linkage 34. For
instance, if linkage 34 is in a fully raised position when the
hovering command is received, implement 34 may be tilted safely at
a relatively slower rate. If linkage 34 is only part way raised, it
may be assumed that implement 36 needs to tilt fairly quickly to
get out of the way as linkage 34 is lowered. These concerns of
course also depend upon how much, if at all, that implement 36
needs to tilt to assume its desired position for hovering. It will
thus be understood that a speed of rotation of each of linkage 34
and implement 36 about the respective axes 42 and 44 defines the
path through space traversed by implement 36. Accordingly, control
signals output to actuator 40 may command a speed of rotation of
implement 36 about axis 44 which is responsive to a commanded speed
of rotation of linkage 34 about axis 42. From Step 155, the process
may proceed to Step 160 at which electronic control unit 74 may
command adjustment of lift arm and/or bucket control valve
actuators 57 and 59. From Step 160, the process may proceed to end
at Step 165. The process might also loop back subsequent to Step
160, to execute again the portion of the control process beginning
at Step 130. As implement system 12 approaches the hovering
configuration, feedback from sensors 76 and 78 may be used in a
closed loop fashion to determine that a set point, i.e. the
hovering configuration, has indeed been reached. In general terms,
the present control strategy may be understood as closed loop
position control, but using the stored gain values as discussed
above as or analogously to feed forward terms to enable implement
system 12 to assume a hovering configuration without colliding with
substrate 200.
[0036] The present description is for illustrative purposed only,
and should not be construed to narrow the breadth of the present
disclosure in any way. Thus, those skilled in the art will
appreciate that various modifications might be made to the
presently disclosed embodiments without departing from the full and
fair scope and spirit of the present disclosure. Other aspect,
features and advantages will be apparent upon an examination of the
attached drawings and appended claims.
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